10 BULLETIN 684, U. S. DEPARTMENT OF AGEICULTUEE. 



LIFE HISTORY. 



In tlie literature pertaining to bitter-rot canl^ers there is very 

 little to be found on the subject of their development and length 

 of life. Spaulding and Von Schrenk (13) state — 



The majority of the cankers found during the last summer probably were 

 started two years ago. During the first year the fung-us made very little head- 

 way. A very small central area was killed, generally around and including a 

 small branch. The following year the large part of the canker was formed. 

 Whether the cankers will continue to increase iu size is as yet undetermined, 

 but it does not seem probable, for if such were the case cankers 3 or more years 

 old ought to have been secured in the orchards where the bitter-rot has been 

 common for many year.s. 



On many varieties the writer has not been able to find any very 

 old cankers, but in the case of very susceptible varieties, such as 

 Givens, he has found many cankers which have attained apparent 

 ages of 8, 10, and more years. One limb, which by count of annual 

 rings was 13 years old, bore a canker which showed 11 zones, in- 

 dicating that the canker had passed through 11 growing seasons. 

 Cankers were found growing on main limbs which were evidently 

 much older than this. In order to trace the development, of cankers, 

 the writer in 1914 made some preliminary inoculations of apple 

 branches with spores from pure cultures of Glomerella cingulata. 

 Inoculations were made by introducing newly formed conidia into 

 small slits artificially made in the bark. The slits were, at once cov- 

 ered with absorbent cotton moistened with distilled water, which was 

 allowed to remain for one week. Controls consisted of branches 

 similarly treated except that no conidia were placed in the slits. 



In Arkansas on September 14, 1914, th^ following inoculations and 

 control experiments were made, using as inoculum conidia from 

 corn-meal cultures of the fungus isolated from a canker on August 3 : 



Three inoculations in slits in 2-year-old branches. 

 One control slit in a 2-year-old branch. 

 One inoculation in a slit in a 1-year-old branch. 

 One control slit in a 1-year-old branch. 



The tree used was a 15-year-old specimen of the Missouri variety. 

 The weather had been hot and moist and accordingly was quite 

 favorable for the developm-ent of the fungus. 



When the absorbent cotton was removed one week later it was 

 evident that the inoculations had been successful. About the slits 

 into which the conidia had been introduced tlie bark was blackened 

 and sunken in a ring from 1 to 2 mm. in width, whereas only the cut 

 surfaces of control slits were blackened. By October 1 the inocu- 

 lated slits formed the central portions of rapidly growing cankers. 

 At that time the fungus on the 2-year-old branches had developed 

 until the blackened, sunken areas had attained lengths varying from 



